The change caused by cables is in most cases caused by varying the capacitance of the setup.
Your cartridge is specified to run at a specific capacitance, your Turntable cables provide usually between 100 and 200pf of capacitance, and your phono stage then adds a further 100 to 300pf.
Many vintage phono stages had switchable phono stage capacitance, so you could switch them between 50/100/250pf
The capacitance will quite substantially change the sound of your setup, and can be used to tune your setup.
Changing cables will invariably change the capacitance - whether it is an improvement or not will then depend on whether you are getting closer to your cartridges ideal setup, or further from it. (and whether you personally like it)
Unless the cables are actually faulty - I would look into cartridge loading (both capacitive and resistive) as this is where the real improvements are to be achieved, rather than messing with the cables.
If your cartridge choice requires lower capacitance, you may then find yourself replacing the cables ! (and cheap video cables make excellent low C TT cables... on a par with Mogami... next step up after that is BlueJeans LC1)
I replaced my cables with a very very short length to achieve 60pf total capacitance, I also use a phono stage with no additional onboard capacitance, and on which I can then plug in whatever capacitance I require.
This way I can go from 60pf to 800pf within a few seconds...
If you run a cartridge that prefers a Low C environment, getting a phono stage where the C load can be turned off will usually gain more than changing the cables.
if you run a cartridge that prefers a high C environment, lowering the cable C may make things sound worse.
hope this helps
Bye for now
David